1. Field of the Invention
The present invention relates to a manually releasable spring-engaged locking device or detent and, more particularly, to a detent mechanism for a pivotable tape cassette compartment of a magnetic tape apparatus which engages itself when the compartment is pivoted into its normal position and which, following manual disengagement, allows the spring-biased compartment to pivot outwardly from the apparatus, for the insertion or removal of a magnetic tape cassette.
2. Description of the Prior Art
Locking devices and detent mechanisms of this type are known from the prior art. They are adapted to the specific structure of the magnetic tape apparatus and especially to the configuration of the tape cassette or tape cassette compartment, as the case may be.
One such configuration, to which this invention is addressed as a preferred application, features a rectangular casing with a flat front wall and a rectangular aperture in the front wall which is occupied by a matching tape cassette compartment. This cassette compartment has a pivot support on one of its two long sides, being carried by a flat chassis of the apparatus and biased to pivot outwardly from the front wall by means of a preloaded spring which is arranged between the cassette compartment and the chassis. The chassis itself is arranged parallel to the casing front wall, at a distance from the latter, carrying the mechanical and electronic working components of the magnetic tape apparatus, including a detent mechanism for the tape cassette compartment.
This known detent mechanism includes a detent groove near the distal end of a short side of the cassette compartment. The lower flank of this detent groove is engageable by a detent pin, which thereby retains the cassette compartment in its normal position in which its outer surface is flush with the outer surface of the casing front wall. The detent pin, extending parallel to the pivot axis of the cassette compartment, is part of a detent slide which is guided for straight-line movements of the detent pin towards and away from the compartment pivot axis. A detent spring urges the detent slide towards the compartment pivot axis, thereby maintaining the detent pin engaged in the detent groove.
For the manual release of this detent mechanism, the prior art apparatus features a slidable release lever which is guided by the casing front wall for movements parallel to the detent slide. This lever includes a finger-engageable button on the outside of the front wall, a lever shaft reaching through a longitudinal guide slot in the front wall, a laterally offset entrainment head on the extremity of the lever shaft, and a guide bracket engaging the lever shaft as a guide counterpart to the button on the inside of the front wall. At assembly, the guide bracket is snapped over the lever shaft, being held in place by means of opposing retaining tongues which engage a shoulder of the lever shaft.
This configuration has the disadvantage of having the button of the release lever as the only part which protrudes over the otherwise even top surface of the magnetic tape apparatus. Additionally, the parts which constitute the release lever are complex in structure and therefore comparatively costly in terms of tooling, if injection-molded in mass production. A removal of the release lever is only possible with considerable skill and the aid of tiny prying tools which must be engaged under the retaining tongues of the guide bracket.